The present invention relates to the field of signal processing for television receivers, and in particular to a method and apparatus for measuring the noise contained in a picture image to be displayed.
Noise reduction algorithms are used to improve the quality of noisy pictures. However, such algorithms reduce the picture quality when the noise level is small. It is therefore desirable to adapt the noise reduction algorithm to the degree of noise contained in the particular picture (i.e., in pictures that are not very noisy, only slight corrections should be made, while in pictures with poor quality, stronger corrections should be made). As a result, the noise contained in the picture must be quantified in order to assess the amount of noise reduction to be applied to the picture.
A standard measure for determining picture quality is often referred to as peak signal-to-noise ratio value (PSNR value). However, this measure requires a reference picture that does not include noise.
In the field of television, a known noise reduction technique includes measuring noise in the blanking interval of the respective TV signal (i.e., in those time intervals in which no active picture content is transmitted). Since the blanking interval of the TV signal is increasingly used for digital services (e.g., to transmit video text information) this technique is no longer available. This problem becomes even more severe since the digital services that use the blanking interval of the TV signal differ from country-to-country.
Therefore, there is a need for an apparatus and method for measuring the noise contained in a picture that does not depend on the blanking interval.